Step 1: When downloaded, install the Flashtool like you install any program on your Window computer.
Step 2: When it is installed, a new folder by name of “Flashtool” will appear in driver where you have installed it. There you will see sub-folders by names of Custom, Devices, Firmwares and Drivers.
Step 3: Now when you need to flash firmware that comes with .ftf extension, you have to place them in firmware sub-folder in Flashtool main folder.
Step 4: Now open Flashtool-drivers to install Fastboot & Flashmode drivers. Once you are done with drivers installation, you are ready to proceed with flashtool. if you are trying to flash a firmware, place the .ftf file in firmware.
Step 5: Run the Flashtool.exe and click on lightening button at top left. Choose Flashmode from popup that appears.
Step 6: Now choose the file that you are flashing and check “APPSLOG”, “CACHE” and “DATA” options. Once done, you will be asked to connect your Sony Xperia phone to your computer with instructions.
Step 7: Follow these instructions like turning off mobile etc and connect it to your computer. Once connected, Flashtool will start flashing on that firmware on your Xperia phone or tablet.